Packaging for fruit-based and/or vegetable-based drinks must firstly conserve the organoleptic qualities of these beverages. Glass packaging is to date the packaging most commonly used, for its gas-barrier properties, but most especially for its high chemical inertness. The general tendency, however, is to replace this material by polymers, which have well known advantages in various respects: lightness, unbreakability.
However, the use of such packaging has hitherto been limited, on account of the drawbacks presented, in particular the loss of organoleptic qualities over time, associated both with the permeability and also with physicochemical interactions between the flavors and the polymer.
Indeed, the use of polymer to package food products often leads to contents/container interaction problems.
These problems are commonly described in the literature and are essentially:
Scalping: i.e. adsorption of constituents of the food on the surface of the material. This leads to a lowering in aromatic intensity and, if the adsorption is selective, to a change in the flavor and the taste. This phenomenon, governed by the partition coefficients of these substances between the food and the material, will be even greater in the case of aqueous foods such as fruit juices.
Absorption: after the adsorption, there may be absorption of the flavorings by the polymer, diffusion into the polymer and then desorption on the outer face. Here also, there will be either a loss or a change in the aromatic intensity.
The chemical reaction between the flavoring and the polymer:
It being sic! possible for the polymer to be both a reactant and a catalyst. The following experiment demonstrates this phenomenon: a model solution of about ten flavorings was placed in contact with a polymer (PP). Gas chromatographic analysis showed that many more substances than the ten or so initially present were then found.
Similarly, a fruit and/or vegetable juice contained in packaging made of polyethylene terephthalate (PET) does not withstand a six-month aging test. Premature oxidation of the packaging is observed in particular.
In order to avoid this drawback, multilayer packaging consisting of an inner layer of an ethylene/vinyl alcohol copolymer coated on either side with a polyethylene film via an intermediate binder has been proposed. However, such packaging is opaque or, in the extreme case, exhibits contact transparency if the polyethylene material is replaced by polypropylene.
Moreover, the extrusion processes used for such packaging are complex, thereby increasing the cost price of this packaging.
Multilayer packaging consisting of an inner layer of nylon (PA) or of an ethylene/vinyl alcohol copolymer coated with two outer layers made of polyethylene terephthalate obtained by a process of co-injection blowing has also been proposed. However, this packaging has a very high cost price owing to difficulties in its manufacture, and is currently virtually abandoned.
Monolayer packaging based on polyethylene naphthalate (PEN), which has excellent qualities of storage and transparency, has also been proposed. However, this packaging is also very expensive, thus limiting its development.
Monolayer packaging based on a PET+PA (polyamide)+cobalt salts alloy, which has excellent qualities of storage and transparency as well as oxygen-absorbing properties, has also been proposed. However, it has never been possible to demonstrate the application of this material in the food sector.
Moreover, it is well known to use a methyl acrylate/acrylonitrile/butadiene copolymer marketed under the trade name Barex 210.RTM. (supplied by the company B.P. Chemicals) for its gas-barrier properties. Such a material has thus already been used as a container for fizzy drinks, as is the case, for example, in U.S. Pat. Nos. 3,862,288, 3,963,399 and 4,054,630.
However, it should be pointed out that the gas-barrier properties are entirely different from those relating to the chemical inertness toward the flavorings. As shown by the many publication sic! mentioned below, this problem, long after the filing of the abovementioned American patents, was not solved.
Mannheim et al., Food and Packaging Interactions, 1988, chap. 6, pages 68-82 studies the interaction between lemon-based products and laminar structures such as polyethylene, polyethylene vinyl alcohol, surlyn (ionomeric resin) and linear low density polyethylene.
Gilbert et al., Instrumental Analysis of Foods, 1983, vol. 1, pages 405-411 study the barrier properties of polymer films toward various aromatic vapors (polypropylene, PVDC, polyethylene).
Matsui et al., J. Agric. Food Chem. 1992, 40, 1902-1905, study the sorption of flavorings by packaging films such as medium density polyethylene and polyethylene vinyl alcohol.
Benet et al., Analysis, (1992) 20, 391-396 studies the interaction of high density polyethylene stoppers with airborne organic substances.